Allow <classifier> inside <plugin> element

In the current Maven project descriptor (http://maven.apache.org/ref/3.0.4/maven-model/maven.html), plugins are declared inside <build> elements by specifying the <groupId>, <artifactId> and <version> elements. However the <classifier> element is currently not legal for a plugin. I would like <classifier> to be legal for plugins, like any other dependencies.

Use case: I maintain two branches for my project: a development branch on JDK7, and a branch ported to JDK6. I use custom Maven plugins for my build process. However the JDK7 doclet API seems to have some incompatible changes compared to the JDK6 doclet API. In addition some APT (Annotation Processing Tools) API are being removed from JDK8, since they are now merged with the javac API. For various reasons (may also be reasons specific to my projects), I wish slightly different Maven plugins depending if I'm building my JDK6 branch or my JDK7 branch. I would like to simply use my custom Maven plugins with the same classifier than the project I'm building, but this is currently not possible.